The present invention relates to variable displacement hydraulic pumps, and more particularly to a control system for varying the displacement of reciprocating piston type pumps.
Various arrangements are known for controlling the displacement of reciprocating piston pumps. Some of these arrangements are shown in U.S. Pat. Nos. 3,995,973, 3,738,111, 3,712,758 and 2,987,003. These patents show various means for controlling pump displacement by limiting the length of the stroke of the pistons. For example, U.S. Pat. No. 3,738,111 shows a means for controlling pump displacement by controlling pressure in the drive chamber of the pump so that the pistons may operate at less than full stroke. U.S. Pat. No. 3,995,973 shows a reciprocating piston type pump having a manually movable control valve which varies the stroke length of the pistons by regulating the quantity and pressure of fluid delivered from a charge system to the inlet of the pump. It is also known to vary the eccentricity of a cam drive mechanism to alter the stroke length of the pistons.
Each of the above-described control arrangements has its advantages and disadvantages depending upon the particular application. There remains a need, however, for a control system for a variable displacement hydraulic pump which is simple in design, sensitive to system variables and provides accurate control of pump displacement over the entire operating range of the pump.